Electrical loads in computer systems and other multi-component electrical systems often use redundant power supplies; that is, they are often coupled to two or more power supplies. This redundancy allows the components to continue uninterrupted operation if one of the power supplies fails and may be important where continued operation of the system is critical or preferable, for example, in systems providing telephone services.
In a traditional method of coupling redundant power supplies to loads in a system, the power supplies are coupled to one or more buses. The loads are then coupled to the buses to receive the power from the power supplies. In such a system, however, there is a danger that a short or over-current situation in a load would damage all power supplies coupled to the load. If all power supplies fail, power could cease on all buses and the entire system would be without power. Thus, a short in only one load could cause a catastrophic failure in which all power supplies fail and power is removed from all the loads in the system.
To prevent such a catastrophic failure, where failure in one of the loads could short out one or more power supplies, each load is typically isolated from the power supplies; that is, a current-limiting device is typically added at each point where the power supplies are coupled to the loads to protect the supplies from a failure in the load. The number of current-limiting devices needed in such a system is typically equal to the number of loads in the system. The use of large numbers of current-limiting devices can result in significant costs.
Another potential issue with this traditional method of supplying power is that if a small number of buses are used in the system, the electrical power passing through each bus may often be greater than the maximum recommended by many safety agencies. As a result, if one of the loads required repair or replacement, power would have to be disconnected from all of the loads to allow safe access to the faulty load.